2012AJ....144...76W

Query : 2012AJ....144...76W

2012AJ....144...76W - Astron. J., 144, 76 (2012/September-0)

"Galaxy," defined.

WILLMAN B. and STRADER J.

Abstract (from CDS):

A growing number of low luminosity and low surface brightness astronomical objects challenge traditional notions of both galaxies and star clusters. To address this challenge, we propose a definition of galaxy that does not depend on a cold dark matter model of the universe: a galaxy is a gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton's laws of gravity. After exploring several possible observational diagnostics of this definition, we critically examine the classification of ultra-faint dwarfs, globular clusters, ultra-compact dwarfs, and tidal dwarfs. While kinematic studies provide an effective diagnostic of the definition in many regimes, they can be less useful for compact or very faint systems. To explore the utility of using the [Fe/H] spread as a complementary diagnostic, we use published spectroscopic [Fe/H] measurements of 16 Milky Way dwarfs and 24 globular clusters to uniformly calculate their [Fe/H] spreads and associated uncertainties. Our principal results are (1) no known, old star cluster less luminous than MV= -10 has a significant ( ≳ 0.1 dex) spread in its iron abundance; (2) known ultra-faint dwarf galaxies can be unambiguously classified with a combination of kinematic and [Fe/H] observations; (3) the observed [Fe/H] spreads in massive ( ≳ 106 M☉) globular clusters do not necessarily imply that they are the stripped nuclei of dwarfs, nor a need for dark matter; and (4) if ultra-compact dwarf galaxies reside in dark matter halos akin to those of ultra-faint dwarfs of the same half-light radii, then they will show no clear dynamical signature of dark matter. We suggest several measurements that may assist the future classification of massive globular clusters, ultra-compact dwarfs, and ultra-faint galaxies. Our galaxy definition is designed to be independent of the details of current observations and models, while our proposed diagnostics can be refined or replaced as our understanding of the universe evolves.

Abstract Copyright: ∼

Journal keyword(s): galaxies: dwarf - galaxies: kinematics and dynamics - galaxies: star clusters: general

CDS comments: UCD 3 is [DJG2000] UCO 3 in Simbad.

Simbad objects: 59

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Number of rows : 59
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20     4.09     ~ 4158 0
2 NAME Mayall II GlC 00 32 46.5323801712 +39 34 40.504803060   14.564 13.807 13.208 12.684 ~ 400 1
3 M 31 AGN 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 13622 1
4 Bol 520 GlC 00 50 42.4580241563 +32 54 58.623459583     15.50     ~ 53 1
5 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 1130 0
6 NAME Sculptor Dwarf Galaxy G 01 00 09.4 -33 42 32   9.79 8.6 8.81   ~ 1498 4
7 NAME Segue 2 G 02 19 16.0 +20 10 31     15.2     ~ 299 0
8 MCG-06-07-001 G 02 39 59.3 -34 26 57   9.02 7.4     ~ 1894 1
9 ACO S 373 ClG 03 38 29.4 -35 27 08           ~ 2029 0
10 CGF 1-4 GlC 03 38 54.0545340024 -35 33 33.320376180   18.5 18.06     ~ 81 1
11 NGC 1851 GlC 05 14 06.76 -40 02 47.6           ~ 1529 0
12 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
13 M 79 GlC 05 24 10.59 -24 31 27.3     8.16     ~ 883 0
14 NGC 2419 GlC 07 38 08.51 +38 52 54.9     10.05     ~ 998 0
15 NAME UMa II Galaxy G 08 51 30.0 +63 07 48     13.3     ~ 410 0
16 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1540 0
17 NAME Segue 1 G 10 07 03.2 +16 04 25     15.3     ~ 517 1
18 2MASS J10081444+1605011 RB? 10 08 14.4415595736 +16 05 01.198034340           ~ 27 1
19 Z 64-73 G 10 08 28.12 +12 18 23.4   11.3 10.0     ~ 1284 1
20 NAME Sextans dSph LSB 10 13 02.9 -01 36 53   12 10.4     ~ 921 0
21 NGC 3201 GlC 10 17 36.82 -46 24 44.9           ~ 1001 0
22 NAME UMa I Galaxy G 10 34 52.80 +51 55 12.0     14.4     ~ 355 1
23 NAME Willman 1 G 10 49 21.0 +51 03 00     15.2     ~ 345 0
24 Z 126-111 G 11 13 28.13 +22 09 10.1   12.9 12.0     ~ 899 0
25 NAME Leo IV LSB 11 32 57.0 -00 32 00     15.1     ~ 419 1
26 NAME Antennae IG 12 01 53.170 -18 52 37.92           ~ 1749 0
27 Cl Melotte 111 OpC 12 11 54.9 +25 16 36           ~ 520 0
28 NAME Coma Dwarf Galaxy G 12 26 59.0 +23 54 15     14.1     ~ 482 1
29 NAME Virgo Cluster ClG 12 30 47.8 +12 23 07           ~ 7107 0
30 M 87 AGN 12 30 49.42338414 +12 23 28.0436859 10.16 9.59 8.63   7.49 ~ 7815 3
31 M 68 GlC 12 39 27.98 -26 44 38.6     7.96     ~ 1069 0
32 NAME CVn II dSph G 12 57 09.6 +34 19 12     16.1     ~ 287 2
33 NGC 5139 GlC 13 26 47.28 -47 28 46.1           ~ 3677 0
34 NAME CVn I dSph G 13 28 03.5 +33 33 21     13.1     ~ 352 1
35 NAME Bootes II G 13 58 00.0 +12 51 00     15.4     ~ 269 0
36 NGC 5824 GlC 15 03 58.612 -33 04 06.70   10.28 9.56     ~ 441 0
37 Z 318-18 G 15 09 08.0 +67 13 21   13.60 10.6     ~ 1459 0
38 Cl Pal 5 GlC 15 16 05.30 -00 06 41.0   15.1       ~ 797 1
39 M 5 GlC 15 18 33.22 +02 04 51.7     5.95     ~ 2095 0
40 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1978 0
41 NAME Hercules Dwarf Galaxy G 16 31 02.0 +12 47 30     14.0     ~ 379 1
42 M 107 GlC 16 32 31.86 -13 03 13.6           ~ 835 0
43 M 12 GlC 16 47 14.18 -01 56 54.7     6.07     ~ 736 0
44 M 10 GlC 16 57 09.05 -04 06 01.1     4.98     ~ 857 0
45 Z 300-12 G 17 20 14.335 +57 55 16.39   12.40 10.6     ~ 1428 1
46 NGC 6388 GlC 17 36 17.461 -44 44 08.34           ~ 988 1
47 NGC 6397 GlC 17 40 42.09 -53 40 27.6     5.17     ~ 2103 0
48 Cl Terzan 5 Cl* 17 48 05.00 -24 46 48.0           ~ 948 1
49 NGC 6441 GlC 17 50 13.06 -37 03 05.2           ~ 940 0
50 M 22 GlC 18 36 23.94 -23 54 17.1           ~ 1459 0
51 M 54 GlC 18 55 03.33 -30 28 47.5           ~ 1164 0
52 NAME SDG G 18 55 19.0 -30 32 43   4.5 3.6     ~ 2438 2
53 NGC 6752 GlC 19 10 52.11 -59 59 04.4           ~ 2121 0
54 M 55 GlC 19 39 59.71 -30 57 53.1     6.49     ~ 913 0
55 M 71 GlC 19 53 46.49 +18 46 45.1           ~ 1190 0
56 NAME Segue 3 Cl* 21 21 31.0 +19 07 02           ~ 75 0
57 M 15 GlC 21 29 58.33 +12 10 01.2           ~ 3274 0
58 M 30 GlC 21 40 22.12 -23 10 47.5     7.10     ~ 1121 0
59 GCl 124 GlC 23 06 44.48 +12 46 19.2   15.6       ~ 307 1

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